CHROMATOGRAPHIC STUDY OF THE NATIVE OXYTOCIC HORMONE OF THE NEUROHYPOPHYSIS

¹ Department of Pharmacology and Experimental Therapeutics, Johns Hopkins University School of Medicine, Baltimore, Maryland

Earlier studies on sedimentation in the ultracentrifuge indicated that the oxytocic hormone in its native state resides in the gland as a large molecular species. The present study, utilizing chromatographic analysis, corroborates the large molecular state of the natural hormone and further, reveals a new oxytocic unit not resolved by previous methods. Dialyzed press-juice was applied to a carboxymethyl cellulose column in 0.005 M phosphate buffer, pH 6.0, and was removed by gradient elution, with salt concentration increasing to 0.5 M NaCl in 0.02 M phosphate buffer, pH 7.5. Three discrete zones of oxytocic activity appeared in the chromatogram. An estimate of molecular size was derived from measurements on the rate of transfer of activity across a cellophane membrane under pressure filtration. Peak 1 material, 80% to 90% of total eluted activity, filtered at the slow rate of a protein; peak 2 activity traversed the membrane at the same rapid rate as synthetic oxytocin; peak 3 activity exhibited an intermediate filtration rate. Peak 2 octapeptide may be generated in the column by dissociation of peak 1 protein. The peak 3 material seems to be a natural constituent in the gland.